The study of sound production by internal flows has a broad range of applications such as: monitoring of respiratory sound of intensive care patients, design of vocal folds prosthesis, design of efficient mufflers, control of the stability of large scale natural gas transport, reduction of pulsations in solid propellant motors of rockets and development of musical sound synthesis based on physical models of woodwind instruments. Our current research is focusing on the aero-acoustical behaviour of corrugated pipes. These pipes are often used in technological applications because they are locally rigid and globally flexible. Whistling of corrugated pipes limits their applicability. Based on the theoretical analysis of systematic experimental work a model is developed, which should support the design of silent corrugated pipes. As a side product we consider the use of corrugated pipes as musical toys.